Systemd timer units

These are the notes of a training course on systemd I gave as part of my work
with Truelite.

.timer units

Configure activation of other units (usually a .service unit) at some given time.

The functionality is similar to cron, with more features and a finer time
granularity. For example, in Debian Stretch apt has a timer for running apt
update which runs at a random time to distribute load on servers:

Note that if you want to schedule tasks with an accuracy under a minute
(for example to play a beep every 10 seconds when running on battery), you need
to also configure AccuracySec= for the timer to a delay shorter than the
default 1 minute.